1. Field of the Invention
The present invention relates to a light guide, an illuminating device and an image reading apparatus, and more particularly to an image reading apparatus configured to optically reading a document image by reading light reflected from the document, and a light guide and an illuminating device suited to be used in such an image reading apparatus.
2. Description of Related Art
An image reading apparatus which is commonly called a scanner illuminates an object to be read with linear light and reads light reflected therefrom. In the past, a fluorescent lamp has been usually used as a source of the linear light illuminating the object to be read. In recent years, however, for the purpose of electric power saving, a movement to replace the fluorescent lamp with an LED is being advanced. An LED is a point light source. Therefore, in order to permit an LED to be used as a light source in an image reading apparatus, as disclosed in Japanese Patent Laid-Open Publication No. 2012-248489, the LED is usually used together with a light guide so that linear light can be achieved. This kind of light guide (which will hereinafter be referred to as a conventional light guide) reflects light emitted from an LED with prisms provided therein and directs the reflected light toward an object to be read. However, from the nature of the conventional light guide to reflect light emitted from an LED with prisms provided therein, it is difficult to achieve proper light quantity distribution on the object to be read, that is, it is difficult to achieve proper light distribution with the conventional light guide.